Bacterial infections in hospital environments are spread by two different ways: external contamination or in vivo contamination from implants. Patients can develop external infections through contact with surfaces such as door handles, pens, telephones, health care workers uniforms (“HCWU”), stethoscopes, or sterile packaging that have been colonized by microorganisms. Hospital-acquired infections (“HAI”) from contact with pathogenic microorganisms affect approximately 2 million people and result in more than 100,000 deaths in the U.S.A. each year. Such infections require 10-20 days of additional patient hospitalization, costing the already strained U.S. health-care systems approximately $25,000-30,000 per infection totaling billions of dollars per year.
The second route for bacteria to infect patients is through hospital invasive support equipment such as intravascular lines and implanted medical devices such as artificial prosthetics, cardiovascular implants and urinary catheters. Implant associated infections (“IAI”) occur in more than one million patients and cost an estimated $3 billion in the U.S. per year. For example, approximately 10-50% of patients with implanted catheters run the risk of developing urinary tract infections (“UTI”) resulting in additional healthcare costs. The rise in the frequency and severity of HAI's and IAI's can be attributed to decreased antibiotic efficacy against drug-resistant strains of pathogens found in surface biofilms.
Biofilm formation involves three phases beginning with the initial reversible adhesion of bacteria on a surface through polysaccharides and adhesion proteins on the bacterial membrane (phase I). Under appropriate conditions, bacteria subsequently firmly attach to a surface (phase II), followed by the secretion of a protective polymeric matrix (biofilm, phase III) in which the bacteria typically show a marked increase in resistance to antibiotics, compared to none-adherent bacteria. As a result, once the infection occurs, it becomes difficult to treat. Thus, strategies that prevent bacterial contamination or destroy adsorbed microorganisms that lead to biofilm formation are actively sought.
Listeria has been observed to increase biofilm production when conditions become more unstable or non-ideal for active growth (Nilsson, R., Ross, T. and Bowman, J. (2011) Variability in biofilm production by Listeria monocytogenes correlated to strain origin and growth conditions. International Journal of Food Microbiology 150. Pages 14-24). It appears that Listeria use biofilm production as a form of defense, and the strength of their survival seems linked to the maturity of the biofilm as does their resistance to antimicrobials.
Biofilms allows for essential cell to cell interactions as well as providing protection to harmful conditions. Listeria biofilms are structurally simple and a mature community can be formed after 24 hours, which is the incubation period of the large droplet tests.
In general, actively growing Listeria cells are susceptible to quaternary ammonium compounds (QACs), even at relative short exposure times over broad temperature and pH ranges. In contrast, it appears that mature biofilms are more resistant against QACs, which suggests that a component of the mature biofilm, potentially an extra-cellular polymeric substance (EPS), could provide protection against QACs. This behavior could be unique to Listeria strains, but there are likely other microorganisms that that possess similar mechanisms for surviving exposure to antimicrobials.
In addition to biofilm maturity, it appears that other factors such as high pH and smooth attachment surfaces may impact on antimicrobial efficacy of QACs against Listeria (Yang, H., Kendall, P., Medeiros and L., Sofos, J. (2009) Efficacy of sanitizing agents against Listeria monocytogenes biofilms on high-density polyethylene cutting board surfaces. Journal of Food Protection, Vol. 72, No. 5, Pages 990-998). Lastly the possibility of non-lethal doses of disinfectants being exposed to the community over time results in resistance by the microbial community (Feliciano, L., Li, J., Lee, J., Pascall, M. (2012) Efficacies of sodium hypochlorite and quaternary ammonium sanitizers for reduction of norovirus and selected bacteria during ware-washing operations. PLOS ONE, Vol 7, Issue 12. E50273). The Listeria strains isolated could be of a stock that has built up these resistances.
In order to prevent the formation of biofilm, strategies have been employed in the past to make surfaces inhospitable to bacteria. For example, small molecule monolayers or polymer thin films either “grafted to” or “grown from” a surface have been widely used to prepare antimicrobial surfaces and clothing. These prior art monolayers or polymer coatings include, for example, non-biofouling coatings which are passive strategies that rely on preventing bacterial adhesion with hydrophobic or zwitterionic thin films, but do not kill the approaching bacteria. A second class of antibacterial thin films kills microbes on contact either by releasing a biocidal agent or immobilizing a biocidal agent. A third class of antibacterial thin films utilize a combination strategy of including a non-biofouling and biocidal component into the coating.
Organophosphorus Antimicrobial Surfaces Based on Monolayers
The first quaternary ammonium phosphonate compounds (phosphonate quats) were disclosed in the early 1950's in U.S. Pat. No. 2,774,786 and Dutch patent NL 79189 for use as synthetic detergents. In the patents syntheses, the final product could only be isolated as a sodium salt of the phosphobetaine after hydrolysis of the phosphonate ester with HCl followed by treatment with NaHCO3. In a similar synthesis Germanaud et al., (Bulletin de la Societe Chimique de France, 1988, 4, 699-704) published the isolation of the phosphonate quats as betaines by purification on an anion exchange resin. The products disclosed in the patents were not spectrally characterized and were used as is, while Germanaud's purification was costly and the product wasn't isolated as a phosphonic acid.
Phosphonate monolayers for the antimicrobial treatment of surfaces have been shown to be advantageous over self-assembled monolayers (SAMs) of thiols and silanes in terms of durability, long-term stability and surface coverage, especially on titanium and stainless steel.
Thiol-based SAM's lack substrate specificity (mainly reserved for gold surfaces) and long-term stability needed for biomedical applications, (i.e. implants). Over time, the thiol-based SAM's become oxidized to sulfonates, which lack affinity for gold and become displaced from the surface.
In comparison to silane based SAM's on metal oxide surfaces, phosphonate based SAM's are advantageous because they resist hydrolysis under physiological conditions and higher surface coverage can be obtained without harsh acid surface pretreatment (to increase the OH content). Siloxanes are also known to be unstable and are easily hydrolyzed under physiological conditions.
Both active and passive strategies to prevent biofilm formation have been described with both mono- and bis-phosphonate monolayers. Examples for active surfaces include contact killing monolayers employing immobilized quaternary ammonium salts and the antibiotic daptomycin. Passive strategies have been described employing hydrophobic perfluorinated bisphosphonates on stainless steel, silicon, and titanium oxidize surfaces for anticorrosion applications.
U.S. Pat. No. 4,101,654 teaches phosphonate-pendant nitrogen heterocyclic compounds that are quaternized by alkyl halides and their use as corrosion inhibitor compounds.
U.S. Pat. No. 4,420,399 teaches phosphonate-quaternary ammonium compounds having a methylene group linking the phosphorus and nitrogen atoms and their use as corrosion inhibitor compounds.
U.S. Pat. No. 4,962,073 teaches porous surfaces treated with phosphoric acid esters.
U.S. Pat. No. 5,770,586 teaches phosphonate/phosphoric acid-quaternary ammonium compounds for use as dental care ingredients and for bone density treatment.
U.S. Pat. No. 5,888,405 teaches methods of inhibiting bacteria from adhering to submerged surfaces using amino-phosphonic acid compounds.
U.S. Patent Application Publication No. 2002/0023573 teaches phosphonate, phosphate and phosphinate compounds linked to mineral oxide surfaces through the oxygen atoms of the phosphorus moieties.
U.S. Patent Application Publication No. 2002/0128150 teaches phosphonate, phosphate and phosphinate sulfur compounds linked to mineral oxide surfaces through the oxygen atoms of the phosphorus moieties.
PCT Application Publication WO 2007/080291 teaches bisphosphonate-amines and quaternary ammonium compounds, their preparation and attachment to metal and metal-oxide surfaces and testing for antibacterial activity.
PCT Application Publication WO 2008/017721 teaches bisphosphonate-amines and quaternary ammonium compounds, their preparation and attachment to silicon and metal surfaces and cell proliferation testing.
U.S. Patent Application Publication No. 2008/0220037 teaches bisphosphonic acid compounds having pendant oxygen, sulfur or at least two quaternary ammonium functional groups, their preparation and treatment of mineral and metal surfaces and antibacterial or biofilm formation testing.
Guerro G et al., Pathologie Biologie, 2009, 57, 36-43 teaches surfaces modified with materials such as phosphonate quaternary ammonium compounds and phosphonate silver coatings, and their bacterial adhesion and inhibition properties.
Queffelec C et al., Chemical Reviews, 2012, 112(7), 3777-3807 teaches phosphonic acids and esters, their synthesis and modification of surfaces using functionalized phosphonic acids and esters. The functional groups include heterocycles, amino groups and larger organic molecules.
Thus, there has been a long-felt need for a durable and environmentally safe antimicrobial metal or mineral surface treatment and a process to manufacture the same, which is more effective against a variety of microbes than existing antimicrobial surface treatments.